Middle tier applications, also referred to as application servers, typically operate on top of a wide range of existing enterprise systems such as database management systems, transaction monitors, and naming and directory services. Many of these application servers are built based on standard specifications such as the Java 2 Platform, Enterprise Edition (J2EE) to provide portability and scalability to applications managing and accessing various enterprise systems.
J2EE, for example, defines a specification for developing enterprise applications to follow as a standard. J2EE bases the enterprise applications on standardized, modular components, by providing a set of services to those components, and by handling many details of application behavior automatically. J2EE includes support for Enterprise JavaBeans (EJB) components, Java Servlets API, JavaServer Pages, and Extended Marked-up Language (XML) technology.
Accordingly, an application built conforming to the J2EE standard specification may be deployed to an application server, local or remote, or a cluster of application servers that supports the J2EE standards, thus allowing the deployed application to manage and access various resources provided by the underlying enterprise systems via the application server.
Clusters are sets of servers that are managed together and participate, for example, in workload management. The servers that are members of a cluster can be on different host machines. An example of an application server that supports clustering is the Websphere application server. Websphere is a set of Java-based tools from IBM that allows customers to create and manage business web sites with Java applications or servlets.
Briefly, deployment is the process of distributing and configuring various part of application programs such as J2EE applications to appropriate locations in application servers. In many cases, deployment process is vendor specific and requires manual steps. Further, deploying applications to a remote or cluster of application servers can require additional knowledge and steps.